(a) Field of the Invention
The present invention relates to a thin film transistor array substrate for a liquid crystal display and a method for fabricating the same.
(b) Description of the Related Art
Generally, liquid crystal displays have a structure where a liquid crystal is sandwiched between two substrates, and an electric field is applied to the liquid crystal to control light transmission. Electrodes are formed on the two substrates, and voltages are applied to the electrodes. One of the substrates has thin film transistors to switch the applied voltages, and is called a “thin film transistor array substrate.”
The thin film transistor array substrate is formed through photolithography using a number of masks. In order to reduce production cost, it is required that the number of masks be decreased.
Meanwhile, the signal lines for the thin film transistor array substrate are usually formed of a low resistance material such as aluminum (Al) or aluminum alloy (Al alloy) to prevent signal delay. However, indium tin oxide (ITO) commonly used for pad portions bears poor contact characteristic with the Al or Al alloy. Therefore, the Al or Al alloy at the pad portions should be replaced with another metallic material such as molybdenum (Mo) or chrome (Cr), and this results in complicated processing steps. In order to solve such a problem, it has been proposed that indium zinc oxide (IZO) should be used to form the pad portions while enhancing reliability thereof. However, in this case, the contact resistance at the pad portions increases while deteriorating the device performance characteristics.